I am using the rest api to trigger builds. It would be extremely helpful to have the plan name available as a runtime variable. currently buildPlanName returns something like "FooProject - trunk - Default Job".

maybe a new variable, such as "buildPlanKey" which would return the name of the project, in the above example it would be FOOPROJECT

In fact, I think all the following should be defined, and maybe others:
projectKey
planName
stageName
jobName